The present invention relates to an improved tool holder and spindle adaptor that can be quickly changed and can be used in operations that require the hole being formed to be within very precise tolerances. For example, in some hole cutting applications, a hole must be cut with very precise dimensions and must be within very strict tolerances. This requires a tool holder and spindle adaptor that are concentric with little or no deflection from the longitudinal center line of the tool. If the tool holder and spindle adaptor are not concentric, the hole being formed will not be within the desired tolerances and will be unacceptable.
There are tool holders and adaptors that can be used to form critical cuts and maintain very strict tolerances. One difficulty with these tool holders and adaptors is that they typically employ a locking taper in order to maintain the necessary concentricity. A locking taper is one that physically locks the tool holder into the adaptor and requires an ejection means such as an ejector pin to release the tool holder from the adaptor. In the locking type tool holders and adaptors, the tool holder has a centering cone that mates with a conical recess in the adaptor. In order to get concentricity, the included angle of the centering cone and conical recess are dimensioned so that there is line contact between the centering cone to ensure that the cone and recess mate and have minimal movement with respect to one another. When the tool holder is properly seated it physically is locked along the line contact to ensure the necessary concentricity.
The primary problem with tool holders and adaptors that have locking tapers is the difficulty in changing the tool because the tool holder is locked in the adaptor. In many operations, there is a need to quickly change the tool and having to eject a locked tool holder can be difficult. Many times the operation has to be shut down in order to change the tool resulting in costly delays.
The assignee of the present invention has patented tool holders and spindle adaptors, known as quick change tool and spindle adaptors, which allow the tool holder to be quickly changed. In these tool holders and spindle adaptors, the tool holder does not lock in the spindle adaptor. These quick change tool and spindle adaptors allow tool holders to be rapidly changed but also quickly centered so that the tool remains centered. But, they do not permit the concentricity required in critical precise operations.
One such patent is U.S. Pat. No. 4,710,079 issued Dec. 1, 1987. The patented tool holder and spindle adaptor permits the tool to be quickly changed and substantially aligned with the longitudinal axis of the power rotated spindle. In order to provide for quick change capabilities, the included angle of the centering cone and conical bearing or conical recess are in the range of 40.degree. to 60.degree. and in the preferred embodiment, approximately 50.degree. . This quick change spindle adaptor employs a tapered collar on the tool holder which extends into the body and is retainingly engaged by a series of spaced balls in the body with the balls projecting into engagement with the sleeve tapered wall to retain the tool holder and shank upon the spindle.
Another example of a quick change tool holder assigned to the assignee of the present invention is disclosed in U.S. Pat. No. 4,834,596 issued May 30, 1989. This tool holder employs basically the same included angle between the conical bearing or conical recess and the cone. The difference between this invention and the prior one is in the locking mechanism to lock the tool holder into the spindle for quick change capabilities. In this quick change spindle adaptor, the spindle has a sleeve secured on it and an outer shell which is rotatably mounted upon the sleeve. Spaced threaded segments are formed on the tool holder and are threadably engaged by the nut for axially anchoring the tool holder upon the spindle and for biasing the centering cone into engagement with the spindle bearing.
Although the above two patented inventions provide for the tool holder to be very quickly changed, the preferred 50.degree. included angle between the centering cone and conical bearing allows movement, although slight, of the tool holder shank within the spindle. Because of this slight movement, there is slight angular deflection of the tool holder and the tool mounted thereon with respect to the longitudinal axis of the spindle. This slight amount of deflection is not a problem in most operations, but is a problem in operations which require specific tolerances.